10,678 research outputs found
Exact and Asymptotic Weighted Logrank Tests for Interval Censored Data: The interval R Package
For right-censored data perhaps the most commonly used tests are weighted logrank tests, such as the logrank and Wilcoxon-type tests. In this paper we review several generalizations of those weighted logrank tests to interval-censored data and present an R package, interval, to implement many of them. The interval package depends on the perm package, also presented here, which performs exact and asymptotic linear permutation tests. The perm package performs many of the tests included in the already available coin package, and provides an independent validation of coin. We review analysis methods for interval-censored data, and we describe and show how to use the interval and perm packages.
Self heating and nonlinear current-voltage characteristics in bilayer graphene
We demonstrate by experiments and numerical simulations that the
low-temperature current-voltage characteristics in diffusive bilayer graphene
(BLG) exhibit a strong superlinearity at finite bias voltages. The
superlinearity is weakly dependent on doping and on the length of the graphene
sample. This effect can be understood as a result of Joule heating. It is
stronger in BLG than in monolayer graphene (MLG), since the conductivity of BLG
is more sensitive to temperature due to the higher density of electronic states
at the Dirac point.Comment: 9 pages, 7 figures, REVTeX 4.
Decoherence processes in a current biased dc SQUID
A current bias dc SQUID behaves as an anharmonic quantum oscillator
controlled by a bias current and an applied magnetic flux. We consider here its
two level limit consisting of the two lower energy states | 0 \right> and |
1 \right>. We have measured energy relaxation times and microwave absorption
for different bias currents and fluxes in the low microwave power limit.
Decoherence times are extracted. The low frequency flux and current noise have
been measured independently by analyzing the probability of current switching
from the superconducting to the finite voltage state, as a function of applied
flux. The high frequency part of the current noise is derived from the
electromagnetic environment of the circuit. The decoherence of this quantum
circuit can be fully accounted by these current and flux noise sources.Comment: 4 pages, 4 figure
Effect of spin orbit scattering on the magnetic and superconducting properties of nearly ferromagnetic metals: application to granular Pt
We calculate the effect of scattering on the static, exchange enhanced, spin
susceptibility and show that in particular spin orbit scattering leads to a
reduction of the giant moments and spin glass freezing temperature due to
dilute magnetic impurities. The harmful spin fluctuation contribution to the
intra-grain pairing interaction is strongly reduced opening the way for BCS
superconductivity. We are thus able to explain the superconducting and magnetic
properties recently observed in granular Pt as due to scattering effects in
single small grains.Comment: 9 pages 3 figures, accepted for publication in Phys. Rev. Letter
Exact and Asymptotic Weighted Logrank Tests for Interval Censored Data: The interval R Package
For right-censored data perhaps the most commonly used tests are weighted logrank tests, such as the logrank and Wilcoxon-type tests. In this paper we review several generalizations of those weighted logrank tests to interval-censored data and present an R package, interval, to implement many of them. The interval package depends on the perm package, also presented here, which performs exact and asymptotic linear permutation tests. The perm package performs many of the tests included in the already available coin package, and provides an independent validation of coin. We review analysis methods for interval-censored data, and we describe and show how to use the interval and perm packages
Impact of disorder on unconventional superconductors with competing ground states
Non-magnetic impurities are known as strong pair breakers in superconductors
with pure d-wave pairing symmetry. Here we discuss d-wave states under the
combined influence of impurities and competing instabilities, such as pairing
in a secondary channel as well as lattice symmetry breaking. Using the
self-consistent T-matrix formalism, we show that disorder can strongly modify
the competition between different pairing states. For a d-wave superconductor
in the presence of a subdominant local attraction, Anderson's theorem implies
that disorder always generates an s-wave component in the gap at sufficiently
low temperature, even if a pure d_{x^2-y^2} order parameter characterizes the
clean system. In contrast, disorder is always detrimental to an additional
d_{xy} component. This qualitative difference suggests that disorder can be
used to discriminate among different mixed-gap structures in high-temperature
superconductors. We also investigate superconducting phases with lattice
symmetry breaking in the form of bond order, and show that the addition of
impurities quickly leads to the restoration of translation invariance. Our
results highlight the importance of controlling disorder for the observation of
competing order parameters in cuprates.Comment: 13 pages, 10 figure
Isotropisation of Generalized Scalar-Tensor theory plus a massive scalar field in the Bianchi type I model
In this paper we study the isotropisation of a Generalized Scalar-Tensor
theory with a massive scalar field. We find it depends on a condition on the
Brans-Dicke coupling function and the potential and show that asymptotically
the metric functions always tend toward a power or exponential law of the
proper time. These results generalise and unify these of De Sitter in the case
of a cosmological constant and of Cooley and Kitada in the case of an
exponential potential.Comment: 10 page
Energy relaxation in graphene and its measurement with supercurrent
We study inelastic energy relaxation in graphene for low energies to find out
how electrons scatter with acoustic phonons and other electrons. By coupling
the graphene to superconductors, we create a strong dependence of the measured
signal, i.e.,\ critical Josephson current, on the electron population on
different energy states. Since the relative population of high- and low-energy
states is determined by the inelastic scattering processes, the critical
current becomes an effective probe for their strength. We argue that the
electron-electron interaction is the dominant relaxation method and, in our
model of two-dimensional electron-electron scattering, we find a scattering
time ps at T=500 mK, 1-2 orders of magnitude smaller than
predicted by theory.Comment: 10 pages, 13 figures submitted to Physical Review
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